Hot wire air flow meter arrangement for monitoring intake air flow rate in internal combustion engine

Abstract

A hot wire air flow meter arrangement comprises a primary and an auxiliary air flow path defined in the air induction passage. A hot wire is provided in the primary air flow path for monitoring air flow rate therethrough. A flow restricting means is provided in the auxiliary air flow path for restricting air flow therethrough. The flow restricting means is selectively operative so that it is effective for restricting air flow in a low engine load condition to force the major part of induction air to flow through the primary air flow path and is not effective at high engine load range so as to minimize flow resistance for induction of sufficient amount of air to an internal combustion engine.

What is claimed is: 
     
       1. A hot wire flow meter arrangement for monitoring an intake air flow rate flowing through an air induction system of an internal combustion engine, comprising: means for defining a measuring portion where the intake air flow rate is to be measured, in said air induction system;   an electrically conductive resistor body disposed within said measuring portion in such an orientation as to subject air flow through said measuring portion;   an electric circuit connected to said resistor body for supplying a controlled voltage for said resistor body for heating the latter at a predetermined temperature, said electric circuit outputting an output signal representative of the voltage supplied to said resistor body; and   means for controlling the path area of said measuring portion in such a manner that the path area of said measuring portion varies at least between a first minimum area and a second maximum area, said path area controlling means being operated to said second position while the engine load is heavier than a predetermined criterion and to said first position while the engine load is smaller than said criterion.   
     
     
       2. A hot wire air flow meter arrangement as set forth in claim 1, which further comprises means for deriving said intake air flow rate on the basis of said output signal of said electric circuit according to a first characteristic when said path area controlling means is placed at the first position and according to a second characteristic when said path area controlling means is placed at the second position. 
     
     
       3. A hot wire flow meter arrangement as set forth in claim 1, which further comprises means for restricting intake air flowing into said first path for regulating air flow through said first path. 
     
     
       4. A hot wire flow meter arrangement as set forth in claim 1, wherein said detecting means detects said engine load condition on the basis of an angular position of a throttle valve disposed in said air induction system. 
     
     
       5. A hot wire flow meter arrangement as set forth in claim 1, wherein said detecting means detects said engine load condition on the basis of an angular position of a throttle valve disposed in said air induction system and an engine revolution speed. 
     
     
       6. A hot wire flow meter arrangement as set forth in claim 1, wherein said detector means detects said engine load condition on the basis of said output signal of said electric circuit. 
     
     
       7. A hot wire flow meter arrangement for monitoring an intake air flow rate flowing through an air induction system of an internal combustion engine, comprising: means for separating a measuring portion where the intake air flow rate is to be measured, into a first and a second paths;   an electrically conductive resistor body disposed within said first path in such an orientation as to subject air flow through said first path;   an electric circuit connected to said resistor body for supplying a controlled voltage for said resistor body for heating the latter at a predetermined temperature, said electric circuit outputting an output signal representative of the voltage supplied to said resistor body;   means for controlling path area of said second path for restricting air flow passing therethrough;   means for detecting an engine load condition for controlling said path area controlling means at least between a first position in which said second path becomes minimum and a second position in which said second path becomes maximum, said detecting means operating said path area controlling means to said second position while the engine load is heavier than a predetermined criterion and to said first position while the engine load is smaller than said criterion; and   means for deriving said intake air flow rate on the basis of said output signal of said electric circuit according to a first characteristic when said path area controlling means is placed at the first position and according to a second characteristic when said path area controlling means is placed at the second position.   
     
     
       8. A hot wire flow meter arrangement as set forth in claim 7, which further comprises means for restricting intake air flowing into said first path for regulating air flow through said first path. 
     
     
       9. A hot wire flow meter arrangement as set forth in claim 7, wherein said detecting means detects said engine load condition on the basis of an angular position of a throttle valve disposed in said air induction system. 
     
     
       10. A hot wire flow meter arrangement as set forth in claim 7, wherein said detecting means detects said engine load condition on the basis of an angular position of a throttle valve disposed in said air induction system and an engine revolution speed. 
     
     
       11. A hot wire flow meter arrangement as set forth in claim 7, wherein said detector means detects said engine load condition on the basis of said output signal of said electric circuit.